1. Field of the Invention
The present invention relates to the structure of valve incorporated in compressors that are used in vehicle air conditioners. More particularly, the present invention relates to a technique for improving the sealing between a valve flap and the corresponding valve seat in compressors. The valve flaps are used to selectively open and close ports for permitting gas flow from a suction chamber to a compression chamber or from a compression chamber to a discharge chamber. The valve flap contacts the valve seat for closing the port.
2. Description of the Related Art
Piston type compressors typically have a valve plate located between compression chambers in the cylinder bores and suction and discharge chambers. A valve plate includes suction ports and discharge ports. The suction ports communicate the compression chambers with the suction chamber and the discharge ports communicate the compression chambers with the discharge chamber. A suction valve flap is arranged opposed to each suction port for selectively opening and closing the port. A discharge valve flap is arranged opposed to each discharge port for selectively opening and closing the port. A valve seat is formed about each port on the valve plate. Contact between a valve flap and the associated valve seat closes the port.
As each piston moves from the top dead center to the bottom dead center in the associated cylinder bore, refrigerant gas in the suction chamber is drawn into the compression chamber through the associated suction port and the associated suction valve flap. As each piston moves from the bottom dead center to the top dead center in the associated cylinder bore, refrigerant gas is compressed in the compression chamber and discharged to the discharge chamber through the associated discharge port and the associated discharge valve flap.
During operation, sliding parts in a compressor such as the pistons and cylinder bores often abrade one another and generate metal powder. If caught between the proximal end of a valve flap and the valve plate, foreign matter such as the metal powder prevents the valve from closing the port. In other words, the foreign matter deteriorates the seal between a valve flap and the associated valve seat. A sealing defect in a suction valve flap causes the refrigerant gas in the corresponding compression chamber to leak into the suction chamber during the compression stroke. A sealing defect in a discharge valve flap causes the refrigerant gas in the discharge chamber to flow back to the corresponding compression chamber during the suction stroke. Such leaking and backflow of refrigerant gas significantly deteriorates the compression efficiency of the compressor.
Japanese Unexamined Patent Publications No. 3-37378 and No. 7-286581 disclose variable displacement compressors that control the discharge displacement of refrigerant gas by adjusting the inclination of a swash plate. In the compressors according to these publications, the above described sealing defects cause the following disadvantages.
Variable displacement compressors often have a drive shaft directly connected to an external drive source such as an engine without a clutch located in between. In such a clutchless system, the compressor is operated even if cooling is not necessary or when frost is being formed in an evaporator. In such a case, the circulation of refrigerant gas between the external refrigerant circuit and the compressor must be stopped. The compressors disclosed in Japanese Unexamined Patent Publications No. 3-37378 and No. 7-286581 stop the flow of refrigerant gas from the external refrigerant circuit into the suction chamber of the compressors, thereby stopping the circulation of the refrigerant gas.
In the compressors according to the above cited publications, the gas flow into the suction chamber from the external refrigerant circuit is stopped when the inclination of the swash plate is minimum. As the swash plate's inclination increases from the minimum, the refrigerant gas again starts flowing into the suction chamber from the external refrigerant circuit. When the swash plate's inclination increases from the minimum, that is, when the displacement of the compressor increases from the minimum displacement, an effective compression needs to be performed. Effective compression here refers to an operation in which refrigerant gas in the compression chamber is discharged to the discharge chamber without backflow of the gas from the discharge chamber to the compression chamber. The above described sealing defects between a discharge valve flap and its valve seat disturbs the effective compression. This affects the capability of the compressor to regain displacement.